This has been driving me crazy for the past few days. I'll try to describe it the best I can~
It's quite a few years old. I remember playing it more than five years ago.

It was a first-person rail shooter, which took place in space.

You play as a human, presumably a marine, with spiky brown hair. Your armor is blue, and so are your friendlies. The enemies are green aliens with teeth. You fight your way through the planet, helping friendlies where you can, and collecting better weapons that you can use until you run out of ammo.

One of the most memorable things about it was this: When you died, you get a cutscene where an alien or two are standing over you, captured. They say something along the lines of "We're gonna have fun with this one" and you get a game over.